Fiber reinforced plastics have found wide spread use in many applications due to their excellent strength to weight ratio as compared to metals and other materials. The demand for some materials, such as carbon reinforced plastics, has increased to the point where fiber supply is challenged and cost has risen accordingly. This has lead to a desire to reuse fibers, particularly carbon fibers, in an effort to augment supply, decrease cost, and convert a material, which is otherwise scrap, into a repurposed component of a product.
The surface of carbon fiber is difficult to work with as there is little that will bond thereto. Carbon fiber is therefore typically treated, in a process referred to in the art as “sizing”, whereby the surface of the carbon fiber is chemically modified to improve the bonding characteristics of the fiber allowing the fiber to be incorporated into a matrix as a reinforcement.
During most carbon fiber recycle operations the sizing is unfortunately removed, or compromised, thereby rendering the carbon fiber very difficult to work with. Carbon fibers with little or no sizing have a low bulk density and the fibers tend to become airborne easily due to the lack of adhesion between fibers. Virgin fiber, which has not been sized, has the same problems and there is a parallel need to utilize virgin fiber along with, or instead of, recycled carbon fiber. Resizing the recycled carbon fibers is not cost effective and not a viable operation commercially.
There is a significant desire in the art for methods to utilize a recycled fiber, particularly with little or no sizing, in a form which is compatible with subsequent operations. The present invention provides fibers, and particularly carbon fibers with little or no sizing, as a thermoplastic bonded preform suitable for use in subsequent applications particularly as a reinforcement in a thermoset matrix composite.